1. Field of the Invention
The invention relates to a recording material for the inkjet printing method, including a substrate and an ink-accepting layer which is applied to at least one side of the substrate, the ink-accepting layer containing an amine-epichlorohydrin condensate and an inorganic pigment. The invention furthermore relates to a process for recording by the discontinuous inkjet printing method, which process uses the inventive recording material.
2. Description of the Related Art
Reaction products prepared on the basis of amine compounds and epihalohydrins are known as assistants for the ink-accepting layers of inkjet recording materials.
For improving the water-insensitivity of printed images which are produced by means of inkjet printers and are intended to be distinguished by outstanding print quality, for example, JP-A-11 277 888 proposes an assistant comprising a linear cationic resin which is formed as the reaction product of an amine component containing a secondary amine with another amine component containing at least two amino groups and an epihalohydrin.
JP-A-11 277 887 likewise relates to an assistant which increases the water resistance and has a different structural formula of the linear cationic resin compared with the document discussed above and a comparable effect which, however, according to the text of the description, is extended to include the reduction of the so-called “ink bleeding” in the case of printed images produced by means of ink-jet printers. In both documents discussed above, the viscosity of the 20% strength aqueous solution containing in each case the proposed assistant is stated as from 50 to 500 mPa·s (B types; 30° C.).
The object of JP-A-10 162 544 is to provide an inkjet recording paper which, in the case of printed images produced using aqueous inks, permits only slight “ink bleeding” and moreover enables a high ink concentration and outstanding water resistance of the printed images. The object is to be achieved by an addition to the coating material in the form of a branched cationic resin which is present as the reaction product of ammonia with at least one preferably primary, secondary or tertiary amine and an epihalohydrin. Furthermore, polyalkylenepolyamine and alkanolamine are preferred as the amine. The viscosity of the 10% strength aqueous solution of this cationic resin is from 1 to 30 mPa·s, measured according to Brookfield (60 rpm/25° C.).
With the aim of presenting a production process for inkjet recording papers on which the ink droplets of aqueous inks bleed only slightly and on which printed images having high ink density and outstanding water resistance are permitted, JP-A-09 240 139 proposes the application of a branched cationic resin which is formed as the reaction product of a polyalkylenepolyamine with an epihalohydrin and, if required, furthermore with an aliphatic amine component. The viscosity of a 10% strength aqueous solution containing the proposed cationic resin is stated as 30 mPa·s, measured according to Brookfield (60 rpm/25° C.).
The teaching of the documents discussed above is that the cationic resins to be used as assistants should suitably be selected in medium molecular weight linear or low molecular weight branched form. On the other hand, these documents provide no information either about possible ratios of the cationic resins to pigments present in the ink-accepting layers or about particular properties of these pigments which are to be established.
According to EP-A-0 914 962, the outstanding inkjet recording property and the superior offset printability of recording material are to be achieved by means of its particularly well bound surface, which moreover has high water resistance. According to the statements of this document, the object is achieved by a linear cationic resin in the ink-accepting layer, inter alia dimethylamine-epichlorohydrin polycondensates being mentioned as examples of this cationic resin. In addition to the cationic resin, the ink-accepting layer furthermore contains binders and optionally pigments. The document gives no information about advantageous properties of the pigments in the ink-accepting layer. Furthermore, this document discloses no advantageous ratios of the cationic resin to other components of the ink-accepting layer.
Finally, EP-A-0 602 326 discloses a quaternary salt of a linear dimethylamine-epichlorohydrin adduct having a degree of polymerization of from 2 to 2 000 as a low molecular weight ink fixing agent in the recording layer of an ink-jet recording paper. In combination with a (meth)acrylamide-diallylamine copolymer, color deviations in applied printed images are to be avoided, in addition to an increase in the ink fixability.
If used at all in the recording layers disclosed there, suitable inorganic and organic pigments are those whose particle size is in a range below 4 μm.
For a long time, pigment-based recording inks were scarcely used instead of inks based on organic dyes, in particular on acidic azo dyes. The problem with this type of recording ink is the low light stability of the organic dyes, associated with the problem of printed images which fade and become discolored, which could be solved to date only unsatisfactorily by means of UV absorbers in the recording inks and by means of ink stabilizers in the inkjet recording materials.
The pigment-based recording inks now more frequently used are substantially more light-stable than the inks discussed above and based on organic dyes, but the pigment-based recording inks have the problem of “ink bleeding”, which is to be understood as meaning the running of different colored printed patterns directly adjacent to one another into one another directly after the printing process. The recording material according to the invention has been developed for use with pigment-based recording inks and significantly reduces the problem of “ink bleeding”.
In inkjet printing, a distinction is made in principle between two different methods of droplet production.
The continuous method provides an ink jet which is ejected under pressure from a nozzle and, owing to the surface tension, separates into very small droplets a certain distance away from the nozzle. The droplets are electrically charged and, depending on the printed image to be produced, are then either deflected into a collecting container or positioned on the recording material by the electric field of electronically controlled deflection plates.
In the discontinuous, so-called “drop-on-demand” method, the ink droplets are produced and ejected from a nozzle, depending on the printed image to be produced, only when an image dot is to be produced on the recording material. One type of “drop-on-demand” printers uses the piezoelectric effect in which an electrically controlled piezoelectric element separates an ink droplet from the reservoir of the recording ink and ejects this droplet from a nozzle. In contrast, “bubble jet” printers use an electrically controlled heating element which allows very small amounts of an aqueous ink to form in a vapor bubble. The resulting vapor pressure ejects the droplet.
The invention relates to recording materials which can be used in both discontinuous methods.